A via is an electrical connection between wiring structures (e.g., wiring layers) in a physical electronic circuit that goes through the plane of one or more adjacent layers. For example, in integrated circuit design, a via is a small opening in an insulating oxide layer that allows a conductive connection between different wiring layers. A via connecting the lowest layer of metal to diffusion or poly is typically called a “contact”.
In via technology, a skip via can be formed through many insulator layers, e.g., bypassing one or more wiring structures within the insulator layers, to connect with a lower wiring structure. This provides improved resistance characteristics, minimizes capacitance for a lower wiring structure, e.g., at M0 layer, as well as provides area efficiencies in the chip manufacturing process.
There are many challenges to using skip vias. For example, in the manufacturing process, e.g., the skip via etching process, the portion of the skip via structure above an upper metallization layer cap can become blown out while trying to open the cap. This damage results in yield loss through shorting to neighboring lines, and also results in a poor skip via profile, making metal fill difficult. These undesirable results decrease device performance. Further, even if the profile of the skip via structure is good, performing a metal fill with conventional physical vapor deposition (PVD) liner seed/copper (Cu) plate approach on a high aspect ratio via is challenging. Further still, having adequate gap fills for minimum insulator spacing is also a concern.